Here is a copy of a post I did before christmas: hope it helps.
As you said, the best way to do this is with an oscilloscope, but to us poorer oiks, this is the next & only way to make sure you dont kill the PS2 laser.
DO NOT TOUCH THE DVD Pot (THE ps2 has a combined CD/DVD laser in one unit, & the adjustments for each are separate - ONLY touch the CD pot!!!
Set your multimeter to Resistance (Ohms).
the laser potentiometer has three pins, one at the top, and two at the bottom. Connect one of the multimeter probes to the pin at the top of the laser pot, and the other to the bottom right pin of the laser pot.
A new PS2 should read about 730 Ohms (as mine did yesterday!!)
I turned the laser pot clockwise about 10 degrees (new reading is now ~600 Ohms (suggested by Adders).
now spend the next hour putting the PS2 back together (mine was in some sort of armour plated stuff (SCPH 30003) and was a complete nightmare to strip down!.
Hey presto - all is cool !!!
Best Regards...Kev1n